1. Field of the Invention
The present invention pertains to cardiac revascularization and more particularly to a procedure for cardiac revascularization involving forming a blood flow path through a heart wall from a heart chamber to a coronary vessel.
2. Description of the Prior Art
Commonly assigned U.S. Pat. No. 5,755,682 and co-pending and commonly assigned U.S. patent application Ser. No. 08/882,397 now U.S. Pat. No. 5,944,019 filed Jun. 25, 1997 (also filed as international application Ser. No. PCT/US97/13980 published as PCT WO 98/06356) teach an implant for defining a blood flow conduit directly from a chamber of the heart to a lumen of a coronary vessel. An embodiment disclosed in the aforementioned application teaches an L-shaped implant in the form of a rigid conduit. The conduit has one leg sized to be received within a lumen of a coronary artery and a second leg sized to pass through the myocardium and extend into the left ventricle of the heart. As disclosed in the above-referenced patent application, the conduit is rigid and remains open for blood flow to pass through the conduit during both systole and diastole. The conduit penetrates into the left ventricle in order to prevent tissue growth and occlusions over an opening of the conduit.
Commonly assigned and co-pending U.S. patent application Ser. No. 08/944,313 filed Oct. 6, 1997 (filed internationally as PCT Ser. No. PCT/US98/17310 published as WO 99/17683) entitled "Transmyocardial Implant" teaches an implant such as that shown in the aforementioned '682 patent '397 application with an enhanced fixation structure. One embodiment of the enhanced fixation structure includes a fabric surrounding at least a portion of the conduit to facilitate tissue growth on the exterior of the implant.
Implants such as those shown in the aforementioned patent applications include a portion to be placed within a coronary vessel and a portion to be placed within the myocardium. When placing a portion of the implant in the coronary artery or other coronary vessel, the artery is incised by an amount sufficient to insert the implant. Preferably, the artery is ligated distal to an obstruction. A transverse incision is made through the artery distal to the ligation. Tools and procedures for such an implantation are shown and described in commonly assigned and copending U.S. patent application Ser. No. 09/063,160 filed Apr. 20, 1998.
In the foregoing references, a constantly open blood flow path is preferred. However, the references also teach a conduit with a valve which closes during diastole. The afore-mentioned PCT/US97/13980 teaches a conduit with a valve which only partially closes during diastole to permit a washing back-flow.
Conduits which include a valve or which otherwise close during the heart cycle are shown in U.S. Pat. No. 5,287,861; U.S. Pat. No. 5,409,019 and 5,429,144 (all to Wilk) and PCT International Publication Nos. WO 98/08456 and WO 98/46115. The alleged benefits of a valve in such a conduit are described in Kashem et al., "Feasibility Study of Left Ventricle to Coronary Artery Perfusion for Severe Coronary Artery Diseases", ASAIO Journal, Vol. 45, No. 2 (March-April, 1999) (Abstract).
Valves in such conduits are difficult to manufacture. For example, such conduits may have internal diameters of 2.0 mm or smaller. The presence of such small valves increase the probability of thrombus.
While a constantly open blood flow path is a presently preferred embodiment which affords amble net forward flow to revascularize the heart, a valve or other structure which at least partially retards retrograde flow during diastole may improve flow. The present invention is directed toward a method of attaining the function and benefits of a valve without the need to fabricate a valve. As will be more fully described, the present invention is directed to a novel implantation technique which induces a tissue response to grow a tissue flap which behaves like a valve.